First check No. 1 and No.4, those are the most probable, but it could be the trans-axle assembly, seeing the age of the machine.
Run the front wheels up onto a sloping area, lay a rug on the ground, and with a flashlight, you can peer under it, and maybe see if the main drive belt is broken.
NOTE:!: Block the wheels, so the durn thing don't run you over!

Assuming this is a hydro, have you checked to see if the drive engage lever under the seat somehow jumped out?

I'am betting that your tractor has a vari-belt drive.
Remove your battery and see if the top belt on the transmission has come off.
I have a 2003 MTD Huskee with vari-drive and the top belt did come off once.
Besides that the transmission has been flawless for 4 1/2 years.

This a hydro, using the rocker pedal for the right foot for forward/reverse. Yes, the lever under the seat was my first thought. It was OK. The design of the gate for that lever makes it impossible to move from one mode to another except deliberately. And the mower could not be pushed until the lever was moved. I pushed it back to the garage by hand. It was moving on level ground when it stopped, no particular stress on the hydro at that moment. Does anyone know from experience if a spring holds the tension on the motion drive idler pulley? If so, a broken spring could cause the problem. I have not yet had time to remove the deck and start repairs.

I have the exact same mower, purchased 5 years ago. This same thing happened to me two years ago, while mowing my front yard -- the mower simply stopped. The belt wheel on the transaxle actualy broke in two, split at the welds. I've always kept this mower in a shed, so rust isn't a big problem, but I think the instant back & forth that the rocker pedal allows puts a little more stress on this than normal. I had to take it to a repair shop to have a new belt wheel installed. Other than that, this has been a great tractor. Which brings me to the reason I found this forum: can anyone tell me how to get the oil filter off this beast? No, it's never been changed...the oil has, but the filter hasn't. The filter appears to have a chrome-colored cover over it (or maybe that's the filter itself), but the replacement filter I have is different (specified in the Murray/Briggs & Stratton manual). I'm clueless as to how to get the old one off and the manual doesn't help.

As far as the oil filter goes, get a strap type oil filter wrench and unscrew it in a counter clockwise direction. It is threaded on just like a bolt. Be sure to put some oil on the gasket of the new filter to help it seal and keep from sticking. It may be on there very tight if it has never been off. It will unscrew though. One last thing, keep the wrench out on the end of the filter, not up in the middle. If you put too much pressure in the middle, the filter can crush. If you stay out on the end it is much stronger.

No filter from the factory, the "shiny" plate is just a bypass, made of diecast "whitemetal". It will break if overtightened. There is a kit that permits installing a filter on that engine, I bought the kit and now have filter on mine. Do not mess with that plate at all until and unless you have the kit in hand. The "belt wheel", does that mean the V-pulley for the motion drive belt?

It's the pulley directly above the transmission, right above the cooling fan. Mine sheared at the weld points.

As to the filter...**no** filter?? Aw, jeez...thanks for the info. Is that kit still available and if so, do you have a "part number" or a name for it so I know what to order? I even gave my Murray parts dealer a picture of the cap, and he's been calling around but even he's stymied by that. Glad to know there's at least one person who understands this engine! Thanks ever so much for the info. Makes one wonder why they describe changing the filter in the engine manual...

My engine is Briggs Model 407600. The blank oil filter cap you now have is part number 710. Removing and reinstalling it is absolutely pointless and probably will destroy it. The adapter nipple to add an oil filter is part 1013. Simply a tube with external threads, overpriced, but essential for adding the filter. I have a lathe, vertical milling machine and 3 types of welding equipment. I probably can deal with pulley problems. I probably will remove the deck, put the mower on jackstands with the rear wheels free to rotate, place a weight on the seat and run the thing while observing the operation underneath. I mention this to perhaps help others and to ask for suggestions on how to diagnose it by better means.

The problem was that a stick had knocked the belt off one of the motion belt idler pulleys. The whole job was not especially difficult nor especially easy. Remove the deck/mower housing. Then the problem was visible. Putting the belt back over the pulley was not possible until I removed the pulley and some other parts. Works OK now. One valuable tool for working on this mower is a cheap Harbor Freight floor jack, such as 36119-6GVA.

I have a Scotts 50560x8 which seems to be a very similar model has recently broken the motion belt. While replacing it, I carelessly did not notice the routing of the belt past the steering gear. The manual says to ensure it is on the left side.....but does that mean left while lying on ones back underneath perspective or looking down from above perspective?

I routed it on the left from the underneath perspective and within 50 yards there was a good deal of smoke from underneath and it stopped moving again. I have not had the chance to take it apart again, but suspect I chose the wrong left side. Anyone know for sure before I climb underneath again?

Left or right is when seated.

Murray manuals are available online at no charge. The belt installation is included.

Here is a link that might be useful: Manuals

I have a 21hp 46" murry garden tractor which the drive belt broke. I really believe murry made this Model impossible to change belt. Is there anyone that could give me heads up on replacing this drive belt?

I need the drive pulley for this model. Does anyone know where I can find one?

long shot, but go here http://www.murray.com/uk/en/support/manuals/ , enter your FULL model # from ID plate on your machine and try to get pulley p/n. Then do a web search for parts suppliers.